Return valve for a hydraulic system

Abstract

A portable one-hand-operable, hydraulic punching machine is disclosed which comprises at least two pumps driven by an electric motor, and a single-acting, spring-return cylinder driven by one of the pumps for a variety of punching operations such as cutting, perforating, and wrenching. The machine has a pump housing and a cylinder housing disposed end to end, with a partition therebetween in which there are formed a fluid supply passageway for supplying a hydraulic fluid under pressure from one pump to the cylinder fluid chamber, a fluid return passageway for returning the fluid from the cylinder fluid chamber to the pump fluid chamber, and a spool chamber open to the return passageway. In order to hold the return passageway closed during cylinder extension, and to open the same for cylinder contraction a return valve is provided which includes a spool reciprocably received in the spool chamber. Normally holding the return passageway open under spring pressure, the valve spool closes the return passageway upon delivery of the fluid under pressure into the spool chamber by the other pump in the pump fluid chamber. A relief valve is provided for bleeding off excess pressure from the spool chamber into the cylinder fluid chamber.

What is claimed is: 
     
       1. A hydraulic system comprising: (a) a pump housing defining a pump fluid chamber to be filled with a hydraulic fluid;   (b) a cylinder housing;   (c) a piston slidably mounted within the cylinder housing and defining a cylinder fluid chamber in combination therewith;   (d) a partition between the pump fluid chamber and the cylinder fluid chamber, the partition having formed therein a first fluid supply passageway for supplying the fluid under pressure from the pump fluid chamber to the cylinder fluid chamber, a fluid return passageway for returning the fluid from the cylinder fluid chamber to the pump fluid chamber, a spool chamber open to the fluid return passageway, a second fluid supply passageway for supplying the fluid under pressure from the pump fluid chamber to the spool chamber, and a relief passageway communicating the spool chamber with the cylinder fluid chamber;   (e) first pump means in the pump fluid chamber for pressurizing the fluid for delivery to the cylinder fluid chamber through the first fluid supply passageway in the partition;   (f) second pump means in the pump fluid chamber for pressurizing the fluid for delivery to the spool chamber in the partition through the second fluid supply passageway;   (g) a spool mounted within said cylinder housing;   (h) first resilient means for biasing said spool in a predetermined direction within said cylinder housing;   (i) said spool being reciprocably mounted in the spool chamber with clearance, said spool holding the fluid return passageway open under the bias of the first resilient means and closing the fluid return passageway against the bias of the first resilient means upon delivery of the fluid under pressure from the pump fluid chamber to the spool chamber by the second pump means; and   (j) relief valve means for holding the relief passageway closed and for opening the relief passageway upon development of fluid pressure in excess of a predefined limit in the spool chamber.   
     
     
       2. The hydraulic system of claim 1 wherein the relief valve means comprises: (a) a valve member movable into and out of sealing engagement with the relief passageway in the partition; and   (b) second resilient means for holding the valve member in sealing engagement with the relief passageway.   
     
     
       3. The hydraulic system of claim 2 wherein the valve member of the relief valve means is a ball to be seated against, and unseated from, an annular valve seat around the relief passageway. 
     
     
       4. The hydraulic system of claim 2 wherein the second resilient means of the relief valve is a leaf spring cantilevered to the partition.